Reflection Loss Performance of Triangular
Microwave Absorber
H. Nornikman, F. Malek, P.J Soh, A.A.H Azremi, A. Ismahayati
School of Computer and Communication Engineering
University Malaysia Perlis
[email protected], [email protected], [email protected],
[email protected]
1. Introduction
In recent years, electromagnetic absorbing materials have been increasingly important in
ensuring successfully of RF anechoic chamber testing performance. Various researches on
enhanced absorber technology have been applied in the testing industry today. Absorbers are one of
the main components in an anechoic chamber which is critical in eliminating reflected signals.
There are two common absorber categories in the electromagnetic wave range, which is in the
microwave range (1 GHz to 300 GHz) and lower frequency range (30 MHz to 1000 MHz).
Microwave absorbing materials that are being used in anechoic chambers such as polyurethane and
polystyrene are able to reduce reflections of high frequency energy. The usefulness of these
microwave absorbers are dependent on testing scopes, either in telecommunication, military, high
speed electronics or automotive.
Absorber shape is the main parameter that affects the performance of microwave absorbers.
The example shapes are layer type absorber, pyramid, wedge, walkway, convoluted, and oblique
absorber. Pyramidal shape absorbers are commonly used for the frequency range between 1 GHz
and 40 GHz. In this paper, a new shape absorber is introducing to improve the reflection loss
performance compare to the existing shape.
The important thing before selected the material is the dielectric constant and tangent loss
of the material. This parameter also can give larger impact to the reflection loss performance. The
dielectric constant is a characteristic quantity of a given dielectric substance, sometimes called the
relative permittivity. Dielectric constant is defined as the relative permittivity ( r) or the absolute
permittivity ( ) relative to the permittivity of free space ( 0). [1] This tangent loss is refers to the
dissipation of power or energy from incident waves. [2]
2. Absorber Design
The triangular base microwave absorber designed using CST Microwave Studio software.
The design concept for this pyramidal microwave absorber is modification from [3-8]. In this paper,
the material of the absorber used is rice husk, a type of agricultural waste. The epsilon, r of this
material is assumed to be equal to 2.9 while the tangent loss, tan of this material is 0.084.
Table 1: Dimension of pyramidal microwave absorber with different base
Dimension (cm)
Part
Equilateral
Isosceles Triangle
Square
Triangle
Base Height
2
2
2
Pyramid
13
13
13
Height
Side length
5.6 (2 sides), 5 (1
5.25 (3 sides)
5 (4 sides)
side)
(a)
(b)
(c)
(d)
Figure 1: Design of microwave absorber in CST Microwave Studios software. (a) Plan view of
array triangular pyramid microwave absorber (b) Perspective view of array triangular pyramid
microwave absorber (c) Plan view of array square base pyramid microwave absorber (d)
Perspective view of array square base pyramid microwave absorber
Figure 1 and Table 1 shows the dimension of the triangular and square base pyramidal
microwave absorber. Isosceles triangle is the triangle with two same sides’ length while other one
side did not have the same length. Equilateral triangle is the triangle that has the same length for its
all sides. Figure 2 shows the parametric study of different side length for triangular base pyramidal
microwave absorber design. In this case ten different lengths from 1 cm to 10 cm are considered to
compare its reflection loss performance.
(a)
(b)
(c)
Figure 2: The parametric study of different side length for triangular base pyramidal microwave
absorber design. (a) Side length = 1 cm (b) Side length = 5 cm (c) Side length = 10 cm
3. Results and Discussion
Figure 2 and Table 2 shows the reflection loss of triangular and square base pyramidal
microwave absorber. From the graph, it shows that isosceles triangle base shows the best average
reflection loss result (in the range between 1 to 20GHz) with - 41.142 dB compare with equilateral
triangle base only - 39.878 and square base with only -39.423 dB. For frequency range between 0.1
to 1 GHz (low frequency range) it shows that triangle shape base can increase the reflection loss
performance compare to square base shape. It achieves - 21.166 dB for isosceles triangle and 21.839 dB equilateral triangle base. Square base shape only shows performance of - 15.883 dB.
Reflection Loss of Triangular and
Square Base Pyramidal Microwave Absorber
-10
equilateral triangle base pyramid absorber
isosceles triangle base pyramid absorber
square base pyramidal absorber
-20
dB
-30
-40
-50
-60
-70
0
5
10
15
20
frequency, GHz
Figure 2: Reflection loss of triangular and square base pyramidal microwave absorber
Table 2: Dimension of pyramidal microwave absorber with different base
Frequency
Reflection Loss (dB)
Range
Isosceles Triangle
Equilateral
Square Base
(GHz)
Base
Triangle Base
0.1 to 1
- 21.166
- 21.839
- 15.833
1 to 5
- 38.518
- 37.235
- 34.736
5 to 10
- 47.091
- 43.653
- 44.170
10 to 15
- 44.014
- 43.294
- 44.175
15 to 20
- 38.529
- 38.457
- 38.485
1 to 20
- 41.142
- 39.878
- 39.423
-38
Average Reflection Loss Effect of Different Side Width
for Isosceles Triangular Base Pyramidal Microwave Absorber
dB
-39
Average Reflection Loss
-40
-41
-42
2
4
6
8
10
Different Side Width (1 cm to 10 cm)
Figure 3: Average reflection loss performance for triangular base pyramid microwave absorber with
different side width (from 1 cm to 10 cm)
Figure 3 and Table 3 shows the reflection loss for triangular base pyramid microwave
absorber with different side width (from 1 cm to 10 cm). It shows that side length = 1 cm shows the
best results with - 40.564 dB while the worst is shown by length = 9 cm with only 39.817 dB.
Table 3: Reflection loss performance for triangular base pyramid microwave absorber with different
side width (from 1 cm to 10 cm)
Side
Reflection Loss (dB)
Width
0.1 to 1
1 to 5
5 to 10
10 to 15
15 to 20
1 to 20
(cm)
GHz
GHz
GHz
GHz
GHz
GHz
1
- 20.743
- 36.634
- 46.633
- 43.730
- 38.501
- 40.564
2
- 21.185
- 37.103
- 44.269
- 44.287
- 38.118
- 40.142
3
- 21.440
- 37.080
- 44.047
- 43.752
- 38.907
- 40.145
4
- 21.604
- 37.153
- 44.038
- 43.174
- 38.971
- 40.051
5
- 21.839
- 37.235
- 43.653
- 43.294
- 38.457
- 39.878
6
- 21.879
- 37.314
- 43.394
- 43.545
- 38.422
- 39.879
7
- 21.955
- 37.446
- 43.334
- 43.165
- 38.409
- 39.848
8
- 21.936
- 37.497
- 43.339
- 43.125
- 38.427
- 39.800
9
- 21.970
- 37.591
- 43.377
- 42.976
- 38.481
- 39.817
10
- 22.023
- 37.700
- 43.478
- 43.019
- 38.633
- 39.820
5. Conclusion
The shape can affect the performance of the absorber. In this case, it shows that the
triangular base shape shows better performance if compare with the existing and commercial square
base shape pyramidal microwave absorber.
References
[1] Bekefi, G. and Barrett, A. H., (1987). Electromagnetic Vibrations, Waves, and Radiation.
Cambridge, MA: MIT Press, NEC2 Modeling of Fractal Element Antennae (FEA), pp. 418420
[2] Neelakanta. P.S., Park J.C., (1995). “Microwave Absorption by Conductor loaded Dielectric”.
IEEE Trans on Microwave Theory and Technique. Vol 43, No 6, pp 1381-1383
[3] H. Nornikman, F. Malek, P. J. Soh, A. A. H. Azremi, F.H Wee, A. Hasnain, “Parametric Study of
Pyramidal Microwave Absorber using Rice Husk”, Progress in Electromagnetics Research, PIER 104,
pg 145-166, 2010
[4] H. Nornikman, P.J Soh, A.A.H Azremi, “Performance Simulation of Pyramidal and Wedge
Microwave Absorbers”, 3rd Asian Modelling Symposium (AMS 2009), Bandung, Indonesia, pg 649 –
654, 25th - 26th May 2009
[5] H. Nornikman, P.J Soh, A.A.H Azremi, F.H. Wee, and M.F.Malek, “Investigation of Agricutural
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Absorber Design using Rice Husk – An Evaluation on Placement Variation”, 2010 Asia-Pacific
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[7] H. Nornikman, F. Malek, P. J. Soh, A. A. H. Azremi, “Effect on Source Signal Condition for
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Communication Engineering (ICCCE 2010), Universiti Islam Antarabangsa (UIA), Kuala Lumpur,
Malaysia, pg 289 – 293, 11th - 13th May 2010
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Engineering and Technology (IET) Brunei Darussalam Network (ICIET 2010), Bandar Seri Begawan,
Brunei Darussalam, 21st - 23rd June, 2010